The killing of 26 people, including 20 children, at Sandy Hook Elementary in Connecticut has understandably shocked the nation, and details are just beginning to emerge about the shooter, Adam Lanza, a 20-year-old man who also murdered his mother. Events like these inevitably reopen debates about gun control, or more tenuously lead people to complain about American culture itself. Yet on the very same day, a 36-year-old Chinese man attacked 22 children with a knife at a primary school in China, suggesting that there is a critical factor with mass homicides that gets far less attention.

For all the disbelief and dismay, we actually know pretty well that most such events are committed by individuals with a particular set of characteristics. As my colleagues Mark Coulson, Jane Barnett and I noted in a 2011 article in the Journal of Police Crisis Negotiations, school shooters have generally been found to 1) have a history of antisocial-personality traits, 2) suffer from mental illnesses such as depression or psychosis and 3) tend to obsess about how others, whether other individuals or society at large, have wronged them. (These conclusions are similar to the findings of a 2002 U.S. Secret Service report on school shootings.) These individuals seethe with rage and hatred and despondency, until they decide to lash out at individuals or a society they believe has done them great wrong. Mental health, as well as our failure to address it as a society, is at the core of these events.

Not all mass homicide perpetrators target schools, but schools do seem to be an unusually common target. People wonder why angry men (and an occasional woman) so often target innocent children who have done them no wrong. In the case of Sandy Hook, although early reports suggested that Lanza’s mother, Nancy Lanza, may have worked there, the school superintendent has since clarified that she was not a teacher or a substitute. In many other cases, there is no obvious connection. Watching the horror and great sadness that has descended over the nation in the past 24 hours, we have our answer. These perpetrators have lashed out against society in the most vicious way possible, inflicting the most pain that they could. That is the point of targeting a school.

Gun control may potentially remove one tool from the hands of potential perpetrators, but mass homicides occur in every part of the globe — Scotland, Norway, Germany, China. So while it may indeed be the right time to talk about gun control, as many are saying, it is also the right time to talk about mental health care in our country. Our country’s funding for mental-health services has only gotten worse since the 2008 recession. As the National Alliance on Mental Illness has been warning for some time, the existing level of funding is inadequate, so our nation’s ability to identify and care for the severely mentally ill has been hamstrung.

In my own clinical work, I’ve seen individuals I’ve identified as being potentially at risk for future criminal behavior because of their mental illness. Very often, there are simply few to no resources for them until they come to the attention of the criminal-justice system. Obviously, the vast majority of the chronically mentally ill won’t commit crimes, certainly not of the severity of the Sandy Hook shooting. But by leaving the mentally ill adrift to fend for themselves, we miss the opportunity to identify and treat some of these at-risk individuals before they escalate. Granted, neither gun control nor a well-funded mental-health system will prevent every mass homicide. But we leave ourselves — and more innocent children — vulnerable until we address both of those issues.